Fabrication of 340-GHz Folded Waveguides Using KMPR Photoresist

Abstract

This letter presents the fabrication of 340-GHz copper folded waveguides (FWGs) using the UV-LIGA method. During the process, KMPR photoresist was employed instead of SU-8 due to its easy removability after electroforming. KMPR patterns with a sidewall height of 300 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> and a trench width of 100 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> were achieved repeatedly under one single-spin deposition and optimized processing conditions, such as UV exposure dose and KMPR bake temperature and time. The dimensional accuracies of the wide side (500 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex> </formula> ) and narrow side (100 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> ) of the copper FWGs were found to be <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\leqslant \hbox{6}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\leqslant \hbox{2}\ \mu\hbox{m}$</tex></formula> , respectively, and the sidewall surface roughness was about 44 nm, with a profile of about 90 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> .